Immunoglobulin, T lymphocytes and the like are not present in the central nervous system and so it is generally thought that immune reactions occur there less readily than in peripheral tissue. It has recently been reported, however, that TGF (transforming growth factor)β, IL-1, IL-6 and other such cytokines and complements have been confirmed present in geriatric maculae—one of the distinctive features of Alzheimer's disease—in addition to β-amyloid protein (Aβ), which is a main structural component thereof; that these are not brought in by peripheral blood but are produced by cells in the brain; and that immune reactions do occur even in the central nervous system. Microglia are thought to be the cells playing the main role in immune reactions in the brain. Microglia cells are present specifically in the brain, are englobing, produce and excrete various cytokines and free radicals, and so forth, and what is known of their nature to date suggests that they are similar in many respects to macrophages. With Alzheimer's disease, a strong activated microglia reaction accompanies geriatric maculae and neurofibrillary degeneration. Removal of the pathological products thereof is thought to be the original purpose of microglia activation, but geriatric maculae and the like are insoluble and therefore untreatable, and, conversely, the complements, cytokines, free radicals and the like produced by the microglia are thought to damage the surrounding neurocytes. For example, it has been reported that microglia activated in vitro by lipopolysaccharide (LPS) and cytokine produce NO and are toxic to neurocytes, or that some of the factors produced are toxic only to neurocytes and have no effect on astrocytes, oligodendrocytes or Schwann cells. There are also reports suggesting the possibility that during the formation of geriatric maculae, also, microglia contribute to the conversion and progression of diffuse plaques that are not toxic to cells, to compact plaques where the surrounding neurocytes are degenerating. Moreover, as there are reports that microglia are activated by Aβ, it has been suggested that microglia activation may be broadly related to neural degeneration in Alzheimer's disease.
It is therefore anticipated that a compound that can suppress microglia activation due to Aβ will be effective as a drug for the prevention or treatment of Alzheimer's disease.
The inventive active component is a pyrimidine derivative, and whereas it is known that pyrimidine derivatives have a vasodilatory effect and a blood pressure-lowering effect (Japanese unexamined patents S51-141896 and S52-116497, and J. Med. Chem. 1980, 23, 927-937), and that they have a beneficial effect against cachexia (Japanese unexamined patent H2-76880), their effect as a drug for central diseases is not known.